Plant hormone response mutants

A variety of plant hormone response mutants has now been described, and is surveyed in this article. In addition to hormone-insensitive mutant phenotypes with defects in hormone-related features, there exist mutants apparently constitutive for the gibberellin responses, and also a mutant hyper-responsive to gibberellin. Although there is still little biochemical evidence on the nature of these mutants, the emerging picture of their genetic dominance relationships has given rise to tentative suggestions of the involvement of represser functions in hormonal control systems.     

Purification of thymocyte growth peptide (TGP) from sheep thymus. Relationship to FTS/thymulin

Thymocyte growth peptide (TGP) initiates DNA synthesis in immature thymocytes and has previously been characterized as an acidic peptide isolated from calf thymus. We now report the isolation of TGP from sheep thymus and show it to be a nonapeptide with a large N-terminal blocking moiety characterized by high UV absorbance. The amino acid composition is identical to FTS, consisting of 2 Gly, 2 Ser, 2 Glx, 1 Ala, 1 Lys, 1 Asx. In contrast to FTS, TGP is acidic with an apparent isoelectric point of 4.2 and a high UV absorbance at 270–280 nm. Reverse phase chromatography of TGP at an acidic pH results in a change of the molecule and the appearance of two new compounds TGP-A and TGP-B, both with less than 50% of the original TGP activity. Full activity could be restored by the addition of ZnCl₂ to TGP-A. Both TGP-A and B have some amino acid composition and high UV absorbance as native TGP. We propose that TGP consists of a non-peptide moiety bound to the N-terminal of the nonapeptide Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn and that the active molecule is stabilized by Zn²⁺.     

Density-induced down regulation of epidermal growth factor receptors

Summary Previous studies have shown that cell density can regulate the binding of several growth factors. To determine whether cell density exerts a uniform effect on the expression of epidermal growth factor (EGF) receptors, seven cell lines were examined in detail. For each cell line, EGF binding was found to decrease as cell density increases. Scatchard analysis of the binding data reveals that decreases in EGF binding are due to reductions in the number of cell surface EGF receptors. The only apparent exception is the effect of cell density on the binding of EGF to A-431 cells. For these cells, increases in cell density lead to two effects: decreases in the number of high affinity EGF receptors and increases in the total number of EGF receptors. In addition to the effects of cell density on EGF receptors, it was determined that increases in cell density can coordinately down-regulate receptors for as many as four different growth factors. Overall, the findings described in this report for EGF and those previously described for transforming growth factor type-β (TGF-β) and fibroblast growth factor (FGF) demonstrate the existence of a common mechanism for down-regulating growth factor receptors. This work was supported by grants from the Nebraska Department of Health (89-51), the National Cancer Institute (Laboratory Research Center Support Grant, CA36727), and the American Cancer Society (Core Grant ACS SIG-16). EDITOR'S STATEMENT The paper by Rizzino et al. demonstrates that receptor number decreases as a function of cell density. This may represent a mechanism by which cell proliferation is reduced as cell density increases.     

Feeding and growth of juvenile sea bass: the effect of ration and temperature on growth rate and efficiency

The effect of ration on the growth of pairs of juvenile sea bass Dicentrarchus labrax fed squid mantle was recorded at four temperatures: 6, 10, 14 and 18) C, covering the range typical of Welsh coastal waters. Initial weight of the fish ranged from 2.8 to 15.9 g. A predictive model for the maximum meal size (M_max) at temperatures between 10 and 18) C, accounted for 95% of the variance in lnM_max. Even when offered excess food, bass at 6) C had a low rate of food consumption [0.19% body weight (BW) day^?1] and lost weight (G=?0.04% day^?1). Predictive regression models for specific growth rate (G) accounted for 86% of the variance at reduced rations and 70% at maximum meals. The relationship between G (calculated for total biomass per tank) and ration was a decelerating curve. G at maximum meals increased with temperature, at lower rations G decreased with temperature. For a pair of bass with a combined weight of 15 g, predicted maintenance ration ranged between 0.7 and 2.3% BW day^?1 and increased with temperature. Maximum meal size was more sensitive to temperature than maintenance ration. At 18) C optimum ration was 7.4% BW day^?1. At lower temperatures, the optimum ration was the maximum meal. The maximum gross growth efficiency was 17.4% at 18) C. Mean absorption efficiency was 94.8%. Ration level had no significant effect on absorption efficiency, which was lowest at 6) C. Condition indices (Fulton condition factor, wet and dry liver—somatic indices and body depth index) increased with meal size at all temperatures except 6) C. An increase in temperature between 10 and 18) C generally resulted in a decrease in condition indices at a given ration. When comparisons were made at a given standard length, gut and carcass weight increased with ration. Visceral fat and gut weight decreased with increased temperature.     

On the biology of bream, Abramis brama (L.) in Lake Peipsi in 1994

The population of bream in L. Peipsi was studied with respect to age, growth rate, condition factor (according to Fulton) and length-weight relationship in 1994. That autumn the bream population in L. Peipsi consisted of fishes aged from 0+ to 15+. During the first year bream reached an average body length of 7.9 cm (the commercial legal size (30 cm) was usually attained by the end of the 5th–6th year. The condition of bream in this lake was above the average of Estonian lakes. The relatively good growth rate and condition of bream in the lake indicates that the waterbody is appropriate for this fish.     

Effects of Nerve Growth Factor and Phorbol Derivative on Reactivation of Herpes Simplex Virus Type 1 in Cultured Cells of Latently Infected Adult Mouse Trigeminal Ganglia

Reactivation of herpes simplex virus type 1 (HSV-1) occurred rapidly in cells of latently infected adult mouse trigeminal ganglia which were cultured in serum-free medium in the presence of sufficient nerve growth factor (NGF). However, HSV-1 reactivation was delayed significantly in ganglionic cultures in the absence of exogenous NGF or in cultures treated with 2-aminopurine in the presence of NGF. The delayed viral reactivation in ganglionic cultures without NGF was accelerated by treatment with phorbol myristate acetate or dibutyryl cyclic AMP. Culture conditions which affected HSV-1 reactivation did not affect replication of HSV-1 in normal ganglionic cultures.     

Phytochrome control of short-day-induced bud set in black cottonwood

In trees and other woody perennial plants, short days (SDs) typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud and bud dormancy. Phytochrome control of SD-induced bud set was investigated in two northern clones of black cottonwood (Populus trichocarpa Torr. & Gray) by using night breaks with red light (R) and far-red light (FR). For both clones (BC-1 and BC-2), SD-induced bud set was prevented when R night breaks as short as 2 min were given in the middle of the night. When night breaks with 2 min of R were immediately followed by 2 min of FR, substantial reversibility of bud set was observed for BC-1 but not for BC-2. By comparing the effects of the R night breaks on bud set and the length of specific internodes, we determined that the R night breaks influenced internode elongation in two opposing ways. First, the addition of a R night break to the SD treatment prevented the cessation of internode elongation that is associated with bud set. Those internodes that would not have elongated under SDs (and would have been found within the terminal bud) elongated in the R treatment. Second, the R night breaks decreased internode length relative to the long-day (LD) control. In contrast to the clonal differences in reversibility that we observed for bud set, the decrease in internode length (i.e. the second effect of R) was R/FR reversible in both clones. Based on these results, we conclude that internode elongation is influenced by two distinct types of phytochrome-mediated response. The first response is a typical response to photpperiod, whereas the second response is a typical “end-of-day” response to light quality. Our results demonstrate that SD-induced bud set in black cottonwood is controlled by phytochrome but that clonal differences have an important influence on the R/FR reversibility of this response. The availability of an experimental system in which SD-induced bud set is R/FR reversible will be valuable for studying the physiological genetics of photoperiodism in trees.     

A cell-based reporter assay for the identification of protein kinase C activators and inhibitors

Transmission of extra cellular signals across biological membranes results in the generation of lipid metabolites which in turn influence specific cellular events such as cell growth or differentiation. Many of these lipid messengers can activate protein kinase C (PKC) isozymes of which one function is to perpetuate the extracellular signals to the nucleus by phosphorylating other targets proteins. We have engineered mammalian cell lines to identify and evaluate activators and inhibitors of PKC-dependent and independent signal transduction pathways. The A31 mouse fibroblast cell line, has been stably transfected with a construct containing a triplet repeat of the TPA response element (TRE) upstream of a thymidine kinase promoter fused to the human growth hormone (hGH) gene. A31 cells containing this reporter construct exhibit significant increases in hGH secretion following stimulation by phorbol esters or other mitogens. The levels of hGH secretion are modulated in this system using different pharmacological agents. We demonstrate that this assay can be used to identify specific and general inhibitors as well as activators of the signal transduction pathway mediated by PKC isozymes. (Mol Cell Biochem141: 129–134, 1994)